This invention relates to a control device for controlling the current supply to the heater for pre-heating the catalyst cleaner of an automotive engine, such that the catalyst is activated when the engine is still cold.
For the purpose of cleaning the exhaust gas of automobiles, catalyst converters including metals exhibiting high catalyst activity, such as platinum, palladium, and rhodium, are provided in the exhaust tube of the automotive engine. The exhaust gas is passed through the catalyst converter and the noxious components, such as hydrogen carbide (HC), carbon monoxide (CO), and nitrogen oxides (NOx), are converted into non-noxious compounds. Namely, the hydrogen carbide and the carbon monoxide are oxidized into water (H.sub.2 O) and carbon dioxide (CO.sub.2), respectively. The nitrogen oxides are reduced to the nitrogen gas.
The catalyst converters for cleaning the exhaust gas exhibit best performance only when the catalyst is heated above a predetermined activation temperature. It is thus generally necessary that the catalyst is kept above 300 degrees Celsius for best performance. When the engine is below the activation temperature immediately after the start, the cleaning efficiency of the catalyst is low. During the time when the engine is operated at a low temperature, a great amount of noxious components such as HC, CO, and NOx are generated. It is thus urgently requested that the catalyst converter be heated to the activation temperature quickly.
Japanese Laid-Open Patent (Kokai) No. 3-31510, for example, proposes to provide the catalyst with a heater. The catalyst is then heated by the heater above the activation temperature to reduce the noxious components released into the air. Further, various proposals are made for determining the appropriate timing for starting the pre-heating of the catalyst. According to such proposals, the catalyst heater is turned on: (1) when the door key is inserted into the lock of the driver's door of the automobile to open it; (2) when the electrical system of the automobile is turned on before the engine is started; or (3) at the same as when the engine is started.
These methods of determining the timings of pre-heating the catalyst, however, have the following disadvantages. According to the first method (1), it is assumed that the engine will be started soon after the door key is inserted into the lock of the door at the driver's seat. However, the insertion of the door key does not necessary mean that the driver is going to start the engine. Thus, if the driver does not start the engine the catalyst heating must be turned off by means of a timer after a predetermined interval. Even then, repeated pre-heating operations are a heavy burden upon the battery. Furthermore, the door lock may be left open. In that instance, the door key is not used at all when the driver gets into the automobile. In the case of the second method (2) by which the pre-heating is started simultaneously when the electrical system is turned on, the battery is placed under a heavy burden if the electrical system includes other loads which are turned on simultaneously. On the other hand, if the catalyst heater is turned on according to the third method (3) when the engine is started, some length of time lapses before the catalyst is heated to the activation temperature. Thus the noxious components within the exhaust gas immediately after the start of the engine cannot be suppressed.